Method for improving the filling capacity of tobacco

ABSTRACT

The invention relates to a process for the improvement of the filling capacity of tobacco such as shredded tobacco leaves or ribs by treatment of the tobacco material having up to approx. 30 wt.-% initial moisture with a treatment gas composed of nitrogen and/or argon at pressures of 50 to 1,000 bar under continuous or stepped compression, followed by a continuous or stepped decompression, the compression and decompression steps taking place in either one autoclave or in cascade-like sequence in several autoclaves, and by subsequent thermal aftertreatment of the discharged tobacco material, which is characterized in that the thermal aftertreatment is carried out with a flowing heat-transferring medium of a mixture of permanent gases and superheated water vapour, wherein the proportion of permanent gas is kept constant at a value in the range from 10 to 60 vol.-%.

[0001] The present invention relates to a process for the improvement of the filling capacity of tobacco according to the preamble of the main claim.

[0002] To improve the filling capacity of tobacco, the INCOM swelling processes according to for example DE 31 19 330 A1, DE 34 14 625 C2 and DE 39 35 774 C2 have proved successful. In these processes, tobacco, say in the form of shredded tobacco leaves or ribs, with an initial moisture of up to approx. 30 wt.-%, is subjected to a continuous or stepped compression with a treatment gas composed of nitrogen and/or argon at pressures of 50 to 1,000 bar, followed by a continuous or stepped decompression. The compression and decompression steps take place either in one autoclave or in cascade-type sequence in several autoclaves. The discharged tobacco material is then subjected to a thermal aftertreatment in which the tobacco swells and the filling capacity of the tobacco thus increases.

[0003] These INCOM processes have proved advantageous compared with the pressure-treatment processes of tobacco with carbon dioxide, ammonia or volatile organic compounds, as with the latter an undesired dissolving of aromas or nicotine from out of the tobacco material must be accepted, or residues of gases in the tobacco material interfere with the taste or because ultimately, when using carbon dioxide, the removal of the dry ice which forms upon decompression is too energy-consuming.

[0004] With regard to the INCOM processes mentioned, DE 31 19 330 describes such an expansion process with working temperatures prevailing in the autoclave of 0 to 50° C., with provision for the use of a tobacco material with a moisture of up to 15 wt.-% and an aftertreatment with water vapour to increase the filling capacity or degree of swelling. Furthermore, DE 34 14 625 C2 and DE 39 35 774 C2 disclose cascade processes in which a low working temperature during the impregnation of the tobacco is effected by cooling the treatment gas before loading the reactor, by cooling the autoclave or by using a supercooled and liquefied treatment gas.

[0005] With these known processes, the thermal aftertreatment is carried out with water vapour of a density of 0.5 to 10 kg/m³, preferably saturated steam, or with hot air of up to 440° C.

[0006] Although a process for the treatment of tobacco with carbon dioxide at pressures of approx. 30 bar is known from EP 484 899 Bl, in which the thermal aftertreatment takes place by feeding the tobacco into high-temperature steam or into a gas containing 50 to 95 vol.-% water vapour upon heating of the tobacco in the flowing medium at 200 to 350° C., water or steam with a lower temperature downstream from the tobacco feeding point being used to reduce the temperature of the flowing medium. The tobacco dried to a moisture of approx. 2 to 3 wt.-% by means of heat-transferring flowing media is then reset to its normal moisture. As dry ice forms upon the pressure treatment of the tobacco with carbon dioxide after the decompression, the tobacco must be heated rapidly for the thermal aftertreatment of the tobacco despite the high evaporation enthalpy of the dry ice, which leads to a considerable thermal and/or mechanical stress of the tobacco.

[0007] In the case of the INCOM process on which the present invention is based, the tobaccos treated with nitrogen and/or argon have a very much lower energy requirement for the desorption of the absorbed gases and the associated swelling of the tobacco than the tobaccos treated with CO₂, so that in the case of the INCOM process, in contrast to the CO₂ process, no adverse effects on taste occur. Furthermore, in the case of the thermal aftertreatment of tobacco treated with nitrogen and/or argon, heat is transferred by the condensation of water vapour on the cold tobacco and in the further course of the thermal aftertreatment the desired moisture content of the expanded tobacco is achieved by drying.

[0008] Nevertheless, also with the INCOM process there exists the danger of over-moistening or overheating the tobacco with the consequence of losses of filling capacity through collapsing of the expanded cell structure.

[0009] The object of the invention is to carry out the thermal after-treatment of the tobacco treated with nitrogen and/or argon in the INCOM process such that a uniform product quality with optimum filling capacity is achieved.

[0010] To achieve this object, a process is therefore proposed according to the preamble of the main claim, which is characterized in that the thermal aftertreatment is carried out with a flowing heat-transferring medium consisting of a mixture of permanent gases and superheated water vapour, wherein the proportion of permanent gas is kept constant at a value in the range from 10 to 60 vol.-%.

[0011] By permanent gas is meant in this context any gas which can be used together with water vapour when drying, such as air, optionally mixed with nitrogen and/or argon or other inert gases.

[0012] Surprisingly, it has been shown that the proportion of permanent gas in the mixture with superheated water vapour is an essential parameter to achieve optimum filling capacity values under the given process conditions and in particular in a stream-drying process.

[0013] Preferably, air is essentially used as permanent gas, the air proportion being controlled indirectly by means of a measurement of the oxygen content. The air proportion of the flowing heat-transferring medium preferably amounts to 20 to 50 vol.-% and in particular 25 to 40 vol.-%.

[0014] Preferably the temperature of the heat-transferring medium is to lie at 120 to 300° C., and the tobacco moisture of the pressure-treated tobacco is to be 8 to 25 wt.-% before the thermal aftertreatment. Furthermore, it is expedient if the tobacco moisture is 8 to 15 wt.-% after the thermal aftertreatment.

[0015] In a particularly preferred embodiment of the process according to the invention, the procedure is that in the thermal aftertreatment, the hot steam is supplied in a closed system according to the known principle of stream drying in which the permanent gas is fed in downstream from the hot-steam feed in the region of the discharge of the heat-treated tobacco and is then circulated in a closed cycle with more water vapour while controlling the constancy of the proportion of permanent gas after cooling of the expanded tobacco and discharging of same. In particular, a rapid lowering of the tobacco temperature and thus the fixing of the filling capacity is thereby achieved.

[0016] In the following, a preferred process using a customary stream-drier is explained with reference to the schematic diagram reproduced in FIG. 1, wherein air was used as permanent gas and its proportion was determined indirectly via an oxygen measurement.

[0017] Depending on local pressure difference between the heat-transferring medium conducted in the cycle and the surroundings, external air is sucked in in the region of the entry (1) and discharge ports (2) and vapours discharged via a vapour flap (3). The feeding-in of the superheated steam takes place via a steam valve (4). The oxygen content in the heat-transferring medium was measured with a probe (5). By control of the steam valve (4) as well as the vapour flap (3), the desired oxygen content and thus a constant ratio of permanent gas to super-heated steam can be established.

[0018] With reference to the following embodiment, the relationship between filling capacity and the permanent gas proportion in the heat-transferring medium is demonstrated. The permanent gas proportion necessary in each individual case to achieve an optimum filling capacity depends on the type and the moisture of the tobacco material used as well as on the boundary conditions of the apparatus.

EXAMPLE

[0019] Tobaccos treated with a stream-drier according to FIG. 1 according to the INCOM process were thermally after-treated as follows. The mass flow of the tobacco introduced was 1250 kg/h, the volume flow of the circulating heat-transferring medium consisting of superheated steam and air 7315 m³/h. The proportion of steam and permanent gas deducible via the measurement of the oxygen content was varied, with constant performance of the heater according to a graduation of the oxygen content of 1.3, 7.5 and 15 vol.-% corresponding to a permanent gas proportion of 6.5 or 37 or 75 vol.-% respectively and an associated contrary change of the initial temperature measured before the introduction of tobacco in the range from 185 to 165° C.

[0020] The filling capacity of the discharged and conditioned tobacco was determined with a Borgwaldt densimeter and the specific volume converted to ml/g at a nominal moisture of 12 wt.-% and a nominal temperature of 22° C. The relative filling capacity improvement was calculated as follows from the data of the basic experiment without permanent gas and the expanded samples with heat-transferring media of steam and permanent gas:

Δ%=(F _(E)-F _(B)) * 100%/F_(B)

[0021] (F_(B)=filling capacity, basic experiment, steam without permanent gas, F_(E)=filling capacity, expanded, steam with permanent gas)

[0022] The diagram shows the relationship between the filling capacity of the expanded tobacco and the process variable of the oxygen content in the heat-transferring medium and the possibility of being able to establish optimum process conditions with the help of this process variable. 

1. Process for the improvement of the filling capacity of tobacco, such as shredded tobacco leaves or ribs, by treatment of the tobacco material having up to approx. 30 wt.-% initial moisture with a treatment gas composed of nitrogen and/or argon at pressures of 50 to 1,000 bar under continuous or stepped compression, followed by a continuous or stepped decompression, the compression and decompression steps taking place in either one autoclave or in cascade-like sequence in several autoclaves, and by subsequent thermal aftertreatment of the discharged tobacco material, characterized in that the thermal aftertreatment is carried out with a flowing heat-transferring medium of a mixture of permanent gases and super-heated water vapour, wherein the proportion of permanent gas is kept constant at a value in the range from 10 to 60 vol.-%.
 2. Process according to claim 1, characterized in that essentially air is used as permanent gas, and the air proportion is controlled by means of a measurement of the oxygen content.
 3. Process according to claim 2, characterized in that the air proportion of the flowing heat-transferring medium is 20 to 50 vol.-%.
 4. Process according to claim 2, characterized in that the air proportion of the flowing heat-transferring medium is 25 to 40 vol.-%.
 5. Process according to claims 1 to 4, characterized in that the temperature of the heat-transferring medium is 120 to 300° C.
 6. Process according to claims 1 to 5, characterized in that the tobacco moisture of the pressure-treated tobacco is 8 to 25 wt.-% prior to the thermal aftertreatment.
 7. Process according to claims 1 to 6, characterized in that the tobacco moisture is 8 to 15 wt.-% after the thermal aftertreatment.
 8. Process according to claims 1 to 7, characterized in that during the thermal aftertreatment, hot steam is supplied in a closed system according to the principle of stream-drying in which the permanent gas is fed in downstream from the hot-steam feed in the region of the discharge of heat-treated tobacco and is then circulated in a closed cycle with more water vapour while controlling the constancy of the proportion of permanent gas after cooling of the expanded tobacco and discharging of same. 